Is TTF1 a good immunohistochemical marker to distinguish primary from metastatic lung adenocarcinomas?

To evaluate the immunohistochemical expression of thyroid transcription fac tor 1 (TTF1) in primary and metastatic: pulmonary adenocarcinomas, and test the diagnostic accuracy of this antibody, two surgical pathologists indepe ndently evaluated 34 cases of adenocarcinomas in the lung without clinical data and tried to distinguish between primary and metastatic cases using hi stological criteria. exclusively. Thirteen cases were primary in the lung a nd 21 were metastases of extrapulmonary adenocarcinomas: 6 from the endomet rium, 4 from the ovary, 3 from the colon, 2 from the kidney, 2 from the bre ast, 2 from the liver and 1 from the prostate. Afterward, the immunoreactiv ity of TTF1 in these neoplasms was evaluated and correlated with morphologi cal and clinical data. The two pathologists were able to diagnose only 5 ou t of 13 cases of primary lung adenocarcinomas (sensitivity of 38.46%) and a lso misdiagnosed two primary malignancies as metastases. After correlation with TTF1 data, the sensitivity increased to 61.53%. The specificity of TTF 1 was 100%. In conclusion, TTF1 is a highly specific marker for primary lu ng adenocarcinomas, and should be included in a panel of antibodies for the differential diagnosis between primary and metastatic adenocarcinomas of t he lung.